Reciprocatory drive mechanism



July 24, 1956 P. H. DIXON 2,755,673

RECIPRDGATCRY DRIVE MECHANISM Filed Jan. 9, 1951 @5 M My United StatesPatent RECIPROCATORY DRIVE NIECHANISM Paul H. Dixon, Rockford, Ill.,assignor, by mesne assignments, to Alice R. Larson, Rockford, Ill.

Application January 9, 1951, Serial No. 2ll5,123

2 Claims. (Cl. 74--57) This invention relates to drive mechanisms inwhich rotary movement of the driving shaft is converted into reciprocatory movement of the driven member, as, for example, a slide,which, in the case of a sander, operates the sanding pad holder that isrigidly secured thereto.

The invention is more particularly concerned with improvementsapplicable to devices of the kind disclosed in the copending applicationof George A. Larson, Serial No. 205,377, filed January 10, 1951.

In the reciprocatory movement transmitted to a sander pad there is atendency to produce noise and transmit excessive vibration to the handleheld by the operator, thus causing too much fatigue when the sander hasto be operated for an hour or so at a time. Such operation is alsoaccompanied usually with excessive wear on the mechanism. It is,therefore, one of the principal objects of my invention to providetransmission gearing ofimproved design between the armature shaft of themotor and the sander pad converting the rotary motion to reciprocatorymotion in such a way that noise and vibration, as well as wear, arereduced to a minimum.

The invention is illustrated in the accompanying drawing, in which Fig.l is a view partly in side elevation and partly in longitudinal sectionon line 11 of Fig. 2 through an electrically driven sander similar tothat disclosed in the copending application but embodying the improveddrive mechanism of my invention;

Fig. 2 is a cross-section on broken line 2-2 of Fig. l, and

Fig. 3 is a horizontal section on line 33 of Pig. 1.

The same reference numerals are applied to corresponding parts in thesethree views.

Referring to the drawing, 1 shall first describe the construction of thesander in general in order that the improvements added by my inventionmay be more fully appreciated and understood. The reference numeral 14designates the housing of an electric motor which, like the end cover15, is substantially fiat on the top and hollowed out on the sides, asindicated at 16 in Fig. 2, to facilitate the operators holding the tooland guiding it easily in its operation. The cover 15 lies substantiallyflush with the housing 14 and serves as an enclosure for thetransmission gearing of my invention indicated at 17, provided betweenthe armature shaft 18 of the motor and a slide 19 that is reciprocablein the base 20 and transmits reciprocatory motion to the pad-holder 21.The latter, it will be understood, may be equipped with any suitable padon the bottom and also with any suitable abrasive clamping means on thetop, so that a sheet of abrasive laid across the pad may be clamped inplace by its end portions which are folded back over the top of the endportions of the plate 21. The base 20 is made up of three plates, 24-26,suitably secured together and to the housing 14 and cover 15, as bymeans of screws 27. The plate 24 has an elongated opening 28 providedtherein through which lubricant from inside the cover 15 is free to Howonto the slide 19 to the far end, the slide being 2,755,673 PatentedJuly 24, 1956 ICC guided for reciprocation in an elongated opening 29pro-- vided in the middle plate 25. The lubricant cannot enter the motorhousing 14, because its bottom wall 30 seals it off, and there is an endplate 31 suitably fixed to the housing 14 supporting one of the bearings32 for the armature shaft 13 serving as a closure for the end of themotor housing inside the cover 5. A spacer 33 of hollow rectangular formis rigidly secured between the slide 19 and pad holder 21 and extendsthrough an elongated opening 34 provided in the bottom plate 26. It isapparent, therefore, that if an adequate supply of semi-fluid lubricantis put in the cover 15 at the time thesander is assembled, thetransmission gearing 17 and the slide 19 will be assured of goodlubrication indefinitely, and, due to the way the slide is enclosed,leaving only a very little of the slide 19 uncovered, there is verylittle, if any, danger of contamination of the lubricant, despite theinevitable dust and grit churned up in the operation of the sander.- Thebearing 32 for the armature shaft 18 will also receive some lubricationthrough the opening 35 in the end wall 31. These features all form apart of the copending Larson application and are claimed therein.

The rotary motion of the armature shaft 18 is converted intoreciprocatory motion of slide 19 by the novel transmission gearing 17 ofmy invention. This gearing includes a pinion 36 suitably formed directlyon the end of the armature shaft 18 and meshing with a gear 37 providedas an integral part of a cylindrical cam 38, the piece 37-33 havingcoaxial journals 39 on the opposite ends thereof received in ballbearings 40, one of which is supported in a recess in the plate 31 andthe other in a recess in the cover 15. The cam 38 is cut away annularly,as at 41, in a plane at an acute angle to the longitudinal axis of thepiece, leaving a connecting center pin 42 in the annular cam track 41thus formed. The connecting pin 42, which is on the axis of generationof the cam track groove 41, is normal to the planes of the two sides ofthe groove and at an acute angle to and intersecting at the mid-point ofsaid pin 42 the axis of revolution of the cam 38. Because of thisinclination of pin 42 with respect to the axis, it will be seen that theflat sides of the groove 41 leave only narrow width flat faces in thegroove at opposite ends of the pin 42 on diametrically opposite sides ofthe cam 38. This connecting center pin 42 intersects at its midpoint theaxis of rotation of the cam 38, so that the cam is truly balanced andwill, therefore, operate smoothly at high speeds and not set up anyvibration. Two semi-spherical bearing balls 43 which are of a diametergreater than the width of said narrow width faces have more than halfthe width of their flat sides slidable on the flat sides of the camtrack 41 while their spherical sides are received with a close workingfit in spheroidal bearing recesses 44 provided therefor in the upwardlyconverging sides 45 of a block 46 that projects into the cam track 41and is riveted, as indicated at 47, to one end portion of the slide 19.It should be clear from this description that in the rotation of the cam38 the semispherical bearing balls 43 sliding on the flat sides of thecam track 41 and using substantially the full width of the narrow flatfaces Will transmit reciprocation to the slide 19 as the semi-sphericalballs oscillate and turn in their bearing recesses 44 in the block 46with a low unit bearing pressure, the continuous oscillation and turningof the semi-spherical balls serving to distribute the wear evenly ontheir fiat sides as well as their spherical slides. The edges of thesemi-spherical balls 43 will, of course, be suitably chamfered to reducefriction and minimize wear. Such chamfering is indicated by the bevellededges 50.

In operation, it should be clear that the gearing 17 of my invention,while highly desirable for a sander drive, is not limited to thatspecific use but may be used whereever a similar drive problem ispresented. The gearing 17 operates much more smoothly and quietly thanmost other reciprocating mechanisms operating at the speeds common forsanders. There is also much less vibration, and the wear is reduced to aminimum because of the fact that surface to surface contact issubstituted for the line contact otherwise obtained where a roller isused as the follower and runs in direct contact with the sides of thegroove. the semispherical bearing elements 43 are universally shiftablein their sockets 44. It is, of course, a much easier matter and,therefore, less costly, to machine the plain groove 41 by a simpleturning operation to get all portions of each side of the grooveaccurately in one plane than to mill out a cam groove of theconventional form. It is also easier by this method to keep withincloser tolerances in quantity production.

It is believed the foregoing description conveys a good understanding ofthe objects and advantages of my invention. The appended claims havebeen drawn to cover all legitimate modifications and adaptations.

I claim:

1. A reciprocatory drive mechanism comprising, in combination, aone-piece cylindrical cam block having means for driving the same, saidblock having an annular cam groove provided therein in a plane at anacute angle to the axis of revolution of the block, each of the sides ofthe groove having all portions thereof in one plane, the opposite sidesof the groove being in parallel planes, the portions of the block onopposite sides of the groove being integrally connected together by alongitudinal center pin portion which is on the axis of generation ofthe groove, its centerline being normal to the planes of the two sidesof the groove and at an acute angle to and intersecting at the mid-pointof said center pin portion the axis of revolu- Furthermore, no bindingis possible, because 4 tion of the block, hearings in which said coaxialjournals are received to support the cam block against endwise movement,a relatively reciprocable block projecting into said groove and havingspheroidal-shaped recesses provided in opposite sides thereof, andsemispherical bearing elements universally oscillatable in said recesseson their semispherical sides and slidable on their fiat sides on theflat sides of the groove, said connecting pin by reason of itsinclination with respect to the axis of the cylindrical block leavingonly narrow-width flat faces in the groove at opposite ends of the pinon diametrically opposite sides of the cylindrical block and saidsemispherical bearing elements being of a'diameter greater than thewidth of said narrow-width faces and being disposed so that more thanhalf of the width of their flat faces is engaged with the fiat sides ofthe groove, thereby utilizing substantially the full width of the narrowfiat faces in the operation of said reciprocatory drive mechanism andcausing continuous turning of said semispherical bearing elements so asto distribute the wear evenly on the flat faces of said elements.

2. A reciprocatory drive mechanism as set forth in claim 1 wherein theedges of the semi-spherical bearing elements are bevelledcircumferentially of the flat sides thereof, substantially as and forthe purpose described.

References Cited in the file of this patent UNITED STATES PATENTS1,132,161 Cassady Mar. 16, 1915 1,351,753 Haver Sept. 7, 1920 1,553,456Metrakos Sept. 15, 1925 2,178,972 Sherman Nov. 7, 1939 2,492,231 MandlDec. 27, 1949

